How severe is CVE-2026-27700?

CVE-2026-27700 has a CVSS 3.x base score of 8.2, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity low, and availability none.

Is CVE-2026-27700 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (15th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-27700?

CVE-2026-27700 affects Hono. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-27700?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-27700 have an EU (EUVD) identifier?

Yes. CVE-2026-27700 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-8644.

When was CVE-2026-27700 published?

CVE-2026-27700 was published on 2026-02-25 and last updated on 2026-06-17.

CVE-2026-27700

CVE-2026-27700 is a high-severity vulnerability in Hono with a CVSS 3.x base score of 8.2. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-290.

Key facts

Severity: High (CVSS 3.x base score 8.2)
EPSS exploit prediction: 0% (15th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-8644
Weakness: CWE-290
Affected product: Hono
Published: 2026-02-25
Last modified: 2026-06-17

Description

Hono is a Web application framework that provides support for any JavaScript runtime. In versions 4.12.0 and 4.12.1, when using the AWS Lambda adapter (`hono/aws-lambda`) behind an Application Load Balancer (ALB), the `getConnInfo()` function incorrectly selected the first value from the `X-Forwarded-For` header. Because AWS ALB appends the real client IP address to the end of the `X-Forwarded-For` header, the first value can be attacker-controlled. This could allow IP-based access control mechanisms (such as the `ipRestriction` middleware) to be bypassed. Version 4.12.2 patches the issue.

Frequently asked questions

What is CVE-2026-27700?: Hono is a Web application framework that provides support for any JavaScript runtime. In versions 4.12.0 and 4.12.1, when using the AWS Lambda adapter (`hono/aws-lambda`) behind an Application Load Balancer (ALB), the `getConnInfo()` function incorrectly selected the first value from the `X-Forwarded-For` header. Because AWS ALB appends the real client IP address to the end of the `X-Forwarded-For` header, the first value can be attacker-controlled. This could allow IP-based access control mechanisms (such as the `ipRestriction` middleware) to be bypassed. Version 4.12.2 patches the issue.
How severe is CVE-2026-27700?: CVE-2026-27700 has a CVSS 3.x base score of 8.2, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity low, and availability none.
Is CVE-2026-27700 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (15th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-27700?: CVE-2026-27700 affects Hono. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-27700?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-27700 have an EU (EUVD) identifier?: Yes. CVE-2026-27700 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-8644.
When was CVE-2026-27700 published?: CVE-2026-27700 was published on 2026-02-25 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:hono:hono:*:*:*:*:*:node.js:*:*

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